Hello!

This fixes an annoyance where a warning would be print every time
ert-runner was executed, like:

--8<---------------cut here---------------start------------->8---
ert-runner --version
Warning: Lisp directory '/tmp/guix-build-emacs-ert-runner-0.7.0.drv-0/ert-runner.el-0.7.0': No such file or directory
Option ‘--version‘ not available
--8<---------------cut here---------------end--------------->8---

Thank you,

Maxim